Technical Field
The present disclosure relates to a method and apparatus for restarting an induction machine, and more particularly, to restarting an induction machine so as to immediately resume an operation of the induction machine with no stop thereof when an instantaneous power failure and the like occur at a 3-phase alternating current power supply of an inverter and then power is restored.
Description of the Related Art
An induction machine is applicable to a variety of range from a fan or a pump to a heating ventilation air conditioning (HVAC) facility. Specifically, an induction machine driving system using an inverter has an advantage of improving energy efficiency so that it is increasingly used.
Generally, when power failure occurs in an alternating current input power supply, an inverter blocks a pulse width modulation (PWM) output within a predetermined time. However, when the power failure is instantaneous or when it takes long time to accelerate a load, it may cause a mass loss in industrial fields to entirely stop and then restart the machine. Therefore, what is required is a method for simply restarting the machine when power is restored while an induction machine is in a free run state.
During power failure, an induction machine turns a free run, and a speed and flux of a rotor are decreased over time. If a voltage for a control is input with no consideration of a varied position and speed information when a machine is restarted, there may be possibility in a generation of a large inrush current or a regenerative power at a capacitor of a direct current stage. That is, when a power voltage of a direct current stage is rising, this may be a fault cause of an inverter so that there is a need for a method for restarting an induction machine without an abrupt rising of a phase current of the induction machine and a power voltage of a direct current stage thereof.
In addition, for this purpose, so as to secure a stable restarting performance of a machine, there is a need for a method for measuring, calculating, or estimating position information of a rotor and speed information thereof when the machine is restarted.
In some embodiments of the present disclosure, since there may be a case in which attaching a rotor position sensor is difficult in some applications of an induction machine, a technology of applying an estimator for obtaining position and speed information of a rotor will be proposed. In addition, a new technology having a configuration capable of preventing a generation of an inrush current and a regenerative voltage when the induction machine is restarted will be proposed.